This invention relates to an engine torque-detecting method and apparatus therefore, and more particularly to an improved method and apparatus for measuring engine torque during running.
It is well known to attempt to improve the efficiency and exhaust emission control of an internal combustion engine to operate it in such a manner as to accurately control the amount of fuel supplied to the engine. Also, other engine parameters are controlled in order to maintain good combustion with the minimum amount of fuel for environmental and efficiency reasons. In order to ensure stable running, however, it is necessary to ensure that adequate amounts of fuel are provided to the engine and that other running conditions are accurately controlled. Therefore, there is a need to measure the actual engine output so as to ensure stability in its operation.
For example, it is known that fuel economy and exhaust emission control may be achieved by operating the engine on a so-called "lean burn" system at least at low and partial lows. With lean burn running the fuel-air mixture supplied to the combustion chamber is less than stoichiometric. However, it is also known that the limits of lean burn may be readily determined by measuring the output torque of the engine. When the output torque falls below a predetermined value it is known that the stability and engine running speed will deteriorate significantly. Therefore, it is desirable to be able to measure the output torque of the engine during its running so as to permit optimization of the lean burn running.
Obviously, it is not possible to measure the engine output in the form of torque through the use of normal measuring apparatus employed for engine testing. That is, the torque-measuring devices used to determine the performance of the engine cannot be incorporated feasibly in a motor vehicle.
There have, therefore, been proposed methods for attempting to measure the engine output torque during its running by measuring some other parameter of the engine. It has been found that pressure in the combustion chamber can be utilized to project engine output torque and ensure stability in running. One method for measuring the engine output torque has been to sample the pressure readings at a number of output shaft angles during a single cycle of operation beginning near the end of the compression stroke and ending during the power or expansion stroke and then predict the engine torque from these readings. However, the necessity of taking multiple readings at varying crank angles provides a very complicated system, and normal computers cannot make the necessary calculations in the time period to adjust the engine to maintain stability without time lags. These problems are particularly acute when the engine is running at a high speed.
It is has also been proposed to measure or estimate the output torque of the engine by measuring the peak combustion chamber pressure. Such a system obviously only requires one pressure reading. However, it has been found that this value is not as closely related to engine output torque as was thought, particularly when cycle-to-cycle measurements are being made and compared with each other.
It is, therefore, a principal object of this invention to provide an improved method and apparatus for measuring the torque output of an engine during its running and per cycle.
It is a further object of this invention to provide an improved method and apparatus for measuring engine torque per cycle that can be utilized with a minimum number of readings.
In conjunction with measuring the torque of the engine and other engine measurements, it is desirable to be able to determine accurately the engine speed. It is commonly the practice to employ with engines a crankshaft or other shaft position detector that outputs a pulse when the shaft rotates to a particular angle. These sensors normally employ a permanent magnet and a related coil, in which the pulse is generated as the magnet and coil are brought into registry with each other. These sensors are normally employed not only to determine a reference angle position for the shaft, such as top dead center, but also to measure engine speed by counting the number of pulses generated in a time period. Although these devices are particularly useful, they provide indications of average engine speed, and not engine speed during a single revolution or a portion of a revolution. With some measurements, such as the measurement of engine torque, it is desirable to measure the instantaneous angular rotational speed of the engine shaft during a single cycle of engine operation.
It is, therefore, a further object of this invention to provide an improved measuring device that can provide not only a reference signal indicative of engine shaft position but also includes means for determining instantaneous engine shaft angular velocity in less than a complete revolution.
As has been previously noted, methods for determining or predicting engine torque have employed sensors for sensing the pressure in the combustion chamber. Such pressure sensors are well known and normally employ piezoelectric devices, which are exposed to the combustion chamber pressure. These devices actually output a first signal that is indicative of the change in pressure exerted on the piezoelectric device. An amplifier circuit is incorporated in conjunction with the piezoelectric device to receive the first signal and convert it into a second signal that will provide an actual pressure reading.
In some instances it is desirable to measure engine torque by actually measuring absolute pressure at certain time intervals. On the other hand, some torque measuring methods may be utilized to measure the accumulated pressure over a time period by integrating a differential pressure signal.
It is, therefore, a still further object of this invention to provide a method for utilizing a pressure sensor to derive either instantaneous change in pressure signals or absolute pressure signals.